Since July 1991, six altimeter missions have been launched successfully, and they have provided almost continuous wave height measurements for more than 12 years. Long-term series of wave height measurements are of major interest for climatology and oceanic wave modeling. Before using such data, the measurements have to be validated, and the homogeneity of the data from various satellites has to be checked. Significant wave height measurements from ERS, TOPEX/Poseidon, GEOSAT Follow-on, Jason-1 and ENVISAT altimeters are validated using cross-altimeter and buoy comparisons. Emphasis is put on the two recent missions Jason-1 and ENVISAT. Corrections for biases and trends are proposed for the six altimeters, allowing the generation of consistent and homogeneous data. Tests of these corrections are performed over global ocean simple statistics. 相似文献
The combination of prevailing northeasterly tradewinds and island topography results in the formation of vigorous, westward
propagating cyclonic eddies in the lee of the Hawaiian Islands on time scales of 50–70 days. These mesoscale (∼102 km) features are nowhere more conspicuous or spin up more frequently than in the Alenuihaha Channel between the Island of
Maui and the Big Island of Hawaii. Cyclonic eddies in subtropical waters such as those around Hawaii vertically displace the
underlying nutricline into the overlying, nutrient-depleted euphotic zone creating localized biologically enhanced patches.
Insight into how these eddies may directly influence pelagic fish distribution is provided by examination of recreational
fish catch data coinciding with the presence of eddies on the fishing grounds. We highlight the 1995 Hawaii International
Billfish Tournament in which a cyclonic eddy dominated the ocean conditions during the weeklong event and the fish catch distribution
differed significantly from the average historical tournament catch patterns. On the tournament fishing grounds, well-mixed
surface layers and strong current flows induced by the eddy's presence characterized the inshore waters where the highest
catches of the prized Pacific blue marlin (Makaira mazara) occurred, suggesting possible direct (e.g., physiological limitations) or indirect (e.g., prey availability) biological
responses of blue marlin to the prevailing environment.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Multiple proton functional group conditional binding constants (K′i) and their concentrations (Ci) are determined from detailed acid/base titration data. The C-K′ information is obtained for kaolinite by assuming that the distribution can be approximated by cumulative independent mono protic groups. Linear programming optimization techniques are used to Fit the data. In addition, the electrode calibration is optimized in the data fit. This adjustment is important for high and low pHs. Discrete concentration dependent pXs of about 3.4, 4.5, 6.7 and 9.8 are determined for a reference kaolinite. These correspond reasonably well to designations made by Wehrli et al. (1990, Aquatic Sciences, Vol. 52, pp. 1–31 ) to A10H2 and AlOH proton reactions at edge and surface sites and to silanol exchange. There is an ionic strength effect for one site. Long and short reaction times and reversibility affect the results. 相似文献
Abstract. Microzooplankton grazing and protozooplankton community structure was investigated in austral summer (Jan./Feb.) and winter (June/July) 1993 in the Atlantic sector of the Southern Ocean during the SAAMES (South African Antarctic Marine Ecosystem Study) Il and III cruises. Grazing was estimated at 22 stations in summer and at 15 stations in winter by employing the sequential dilution technique. Nano-heterotrophic flagellates (< 20 μm) and ciliates (aloricate ciliates and tintinnids) dominated the protozooplankton assemblages along both transects. Densities in winter were, however, nearly an order of magnitude lower than in summer. Microzooplankton grazing removed between 0 and 28% (mean = 13.2%) of the initial phytoplankton stock in summer and, between 24 and 51 % of the initial stock (mean = 37.6%) in winter. The potential primary production removed during summer ranged between 0 and 46% (mean = 22.0%) compared with the winter range of 56–83% (mean = 67.2%). Size selectivity grazing experiments conducted during both studies suggest that microzooplankton preferentially graze on the nano- (20–2.0μm) and picophytoplankton (2.0–0.2μm) size fractions. These results have important implications for the efficiency of the carbon pump in the Southern Ocean. During summer when the larger cells dominate phytoplankton biomass, the bulk of the photosynthetically fixed carbon appears to be channelled to the meso- and macrozooplankton fractions. This results in a rapid transfer of organic carbon out of the zone of regeneration to the deep ocean via vertical migration and large faecal pellet production. During winter, however, an increase in the contribution of the smaller size fractions to total phytoplankton biomass results in a greater proportion of the photosynthetically fixed carbon being channelled to the microzooplankton fraction. The efficiency of the carbon pump is, therefore, reduced in that the transfer of carbon below the zone of regeneration is reduced as carbon is recycled mostly within the microbial loop in the upper mixed layer. 相似文献
A study has been made of the orientation of the spurs of the outer front of a barrier coral-reef tract in the Bay of Tuléar on the southwest coast of Madagascar. All types of coral reef tracts are present: outer or barrier reefs, lagoon reefs and coral banks. The orientation of the spurs was studied as a function of the direction of the swell crests which are either parallel or oblique to the alignment of the reef front of the “Grand Récif” which extends over 18 km. When the swell is oblique, the spurs are not, as is generally held, perpendicular to the crests of the swell. The orientation of the spurs is a resultant direction between the direction of the swell orthogonals and the direction of the slope of the outer reef flat. From aerial photographs one can determine the directions of the spurs and of the slope of the outer reef flat. It is easy to obtain the direction of the crests of the swell and then to construct the wave diagram. The morphological aspects and the distribution of the deposits on the inner flat of the coral reef tract depend on the orientation of the swell.
Résumé
L'étude de l'orientation des éperons d'un front récifal externe a été réalisée dans la baie de Tuléar sur la côte sud-ouest de Madagascar. Dans ce secteur, tous les types d'édifices récifaux sont présents: récifs barrières externes, récifs de lagon et bancs coralliens. Nous avons étudié l'orientation des éperons en fonction de la direction de la houle qui est soit parallèle, soit oblique par rapport au front récifal du Grand Récif qui s'étend sur 18 km. Quand la houle est oblique, les éperons ne sont pas — comme on le dit généralement — perpendiculaires à la houle, mais leur orientation est une direction résultante entre la direction de propagation de la houle et celle de la pente du platier récifal au point considéré. Sur les photographies aériennes, on détermine la direction des éperons et celle de la pente. Une construction simple permet d'obtenir la direction de la crête des vagues et de construire le plan de vagues. Toute la morphologie et la répartition des dépôts du platier d'un édifice récifal sont sous la dépendance de l'orientation de la houle. 相似文献
The dynamically coupled interaction between the hull of a floating platform and its risers and tendons plays an important role in the global motions of the platform and the tension loads in the tendons and risers. This is an especially critical design issue in the frequency ranges outside the wave frequencies of significant energy content. This study examines the importance of this coupled dynamic interaction and the effectiveness of different approaches for their prediction. A numerical code, named COUPLE, has been developed for computing the motions and tensions pertaining to a moored floating structure positioned and restrained by its mooring/tendon and riser systems. In this study the experimentally measured motions of a mini-TLP are compared with those computed using COUPLE and alternative predictions based upon quasi-static analysis. The comparisons confirm that COUPLE is able to predict the dynamic interaction between the hull and its tendon and riser systems while the related quasi-static analysis fails. The comparisons also show that wave loads on the mini-TLP can be accurately predicted using the Morison equation provided that the wavelength of incident waves is much longer than the diameters of the columns and pontoons and that the wave kinematics used are sufficiently accurate. Although these findings are based upon the case of a mini-TLP, they are expected to be relevant to a wide range of floating or compliant deepwater structures. 相似文献